Abstract
Aim: Identifying genetic groups within species' ranges is critical for inventorying diversity and delineating conservation units. For many North American amphibians, limited knowledge of genetic structure in Canada constrains effective conservation decision-making. The western toad (Anaxyrus boreas) has an extensive distribution in western North America and, with a large part of its range in Canada, represents an opportunity to fill gaps in our understanding of genetic structure in this part of the country. Curiously, toads to the east of the Canadian Rocky Mountains (CRMs) have a vocal sac and produce a distinct advertisement call, whereas toads to the west of the CRMs and in southern parts of the species' range lack these traits. We aimed to evaluate genetic structure across the Canadian range of western toads to determine whether these ‘Calling’ and ‘Non-calling’ populations are genetically distinct.
Location: British Columbia and Alberta, corresponding to east–west coverage of the Canadian range of western toads.
Methods: We genotyped individuals using reduced representation sequencing (ddRAD-seq) and used population genomic methods to quantify genetic structure. We examined spatial agreement between observed genetic groups and the distribution of calling and non-calling individuals based on the original phenotypic data used to describe these groups. Finally, we used ecological niche models to explore differences in climatic space occupied by each population and test whether climate barriers may play a role in shaping genetic boundaries.
Main-Conclusions: Our results show that Calling and Non-Calling populations of western toads in Canada not only differ in key reproductive traits, but represent distinct genetic groups separated by an area of low climatic suitability. We additionally find support for a third, undescribed genetic group in the southern CRMs. These results contribute to our understanding of genetic structure in Canada and highlight the potential for additional, overlooked groups within the northern parts of species' ranges.